Circuit breaker



Jan- 21, 1947. M. asl-:ORN ETAL 2,414,526

CIRCUIT BRAKER Filed Dec. 8, 1942 Patented Jan. 2l, 1947 UNITED STATES PATENT OFFICE CIRCUIT BREAKER Pennsylvania Application December 8, 1942, Serial No. 468,234

(Cl. 20G-88) 17 Claims.

time delay tripping on overloads up to the instantaneous tripping current.

Another object of the invention is to provide a circuitA breaker with an improved trip device comprising an electromagnet having a plurality of. movable core members, one of said core members being. operable at times independently of a second core member, and at other times both core members operate simultaneously to trip the breaker.

Another object of the invention is the provision of a circuit breaker having an improved trip mechanism of simple and economical construction wherein a current responsive bimetal element acts through an ambient compensating bimetal to operate a latch and release a movable core member of an electromagnet to thereby effect trippingr of the breaker.

Another object of the invention is the provision of a circuit breaker with an improved trip device comprising a solenoid having two movable core members which are operated at times simultaneously after a time delay to trip the breaker, and

vat otherv times one of the core members is operated independently of the other core member to instantaneously trip the breaker.

Another object of the invention is to provide a circuit breaker with an improved trip device including an electromagnet having interchangeable energizing coils of various ampere ratings and wherein the magnetic air gap may be varied according to the rating of the coils so that the same trip. device may be used for a large number of different circuit breaker ratings.

Another object of the invention is to provide a circuit breaker with an improved trip device including a tripping solenoid having a latched armature the position of which may be adjusted to change the air gap without changing' the latch relation.

Another object of' the invention is to provide a circuit breaker with an improved thermal-magnetic trip device wherein a relatively light force is required of the thermal element to effect tripping of the breaker.

Another object of the invention is to provide a circuit breaker with an improved trip device which is simple, accurate and reliable in operation and inexpensive to manufacture.

The novel features that are considered characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to structure and operation together with additional objects and advantages thereof will be best understood from the following detailed description of one embodiment thereof when read in conjunction with the accompanying drawing, in which:

Figure 1 is a side elevational view, partly in section, of a circuit breaker embodying the principles of the invention;

Fig. 2 is a horizontal sectional View taken on line II-II of Fig. l, and showing substantially a bottom view of the trip device.

Referring to Figure 1 of the drawing, the reference numeral Il designates a base of strong insulating material which supports the various parts of the circuit breaker. A pair of terminals i3 and I5 are suitably secured to the base and each terminal has one or more terminal studs i9 secured thereto which extend through the back of the base l I and serve to electrically connect the breaker to the circuit which it controls.

The upper terminal I3 has a contact block 2| oi' rigid conducting material secured thereto; and a rigid contact block 23 secured to the base is electrically connected to the lower terminal I5 through the energizing winding of the trip device of the breaker, which will be hereinafter described.

The specific structures of the contact means and operating mechanism Of the circuit breaker as shown, are of the same construction as the contact means and operating means fully disclosed in Patent No. 2,214,471 issued September 10, 1940, to Leon R. Ludwig and Merl E. Horn, and assigned to the assignee of the present invention. Hence only a brief description of these parts will be given in this application.

The main stationary contacts 25 and, 27 are rigidly secured to the contact blocks 2l and 23, respectively; and the auxiliary stationary contacts 29 and 3l are secured to a triangularlyshaped contact platform 33' of conducting material which is mounted on the upper portion of the b-lock 2| for limited tilting and rocking movement by means of pins 35 projecting from the opposite sides of the platform which engage in slots 3l provided in a pair of side walls 39 secured to the block 2|. The platform 33 is biased outwardly from the base by a plurality of springs 4| and 53, and outward movement of the platform is limited by the engagement of the pins 35 with the outer ends of the slots 31 and by stop projections 35 carried by the platform adjacent its upper end. The platform 33 and, consequently, the auxiliary contacts 29 and 3| are electrically connected to the terminal I3 by means of a flexible shunt conductor 41.

The movable contact means of the circuit breaker comprises a channel-shaped contact arm 99 of conducting material which is rigidly secured to a pivoted switch member 5| by means of a plurality of screws 53. The contact arm 49 carries a main contact bridging member 55 for bridging the main contacts 25 and 21, and an auxiliary contact member 51 for engaging the stationary auxiliary contacts 29 and 3|, the auxiliary contact member 51 being secured to the upper end of the channel-shaped contact arm 49 by a plurality of screws 59.

The main contact bridging member 55 is formed of rigid conducting material, and is loosely mounted. on the contact arm 49 for limited movement relative to the contact arm toward and away from the main contacts 2'5 and 21 by means of a pair of studs 6| secured to the Contact carrying arm 59, only one stud being shown. The free ends of the studs 6| have a pair of nuts 63 mounted thereon for limiting inward movement of the bridging member 55 toward the main contacts 25 and 21. A pair of coil springs 65 encircle the studs 5|, and are disposed between the contact carrying arm 49 and the bridging member 55 for biasing the bridging member toward the stationary main contacts 25 and 21 with a predetermined force. The ends of the bridging member 55 are beveled to lie parallel with the beveled edges of the contact blocks 2| and 23, and have a pair of contacts 61 secured thereto for engaging the main stationary contacts 25 and 21.

The auxiliary contact member 51 is formed of rigid conducting material, and has an intermediate contact 39 and an arcing contact 1| secured thereto for engaging the intermediate and arcing contacts 29 and 3| of the stationary contact means. y

A common iiexible shunt conductor 13 electrically connects the auxiliary contact member 51 to the main stationary contact block 23. The flexible conductor 13 has its upper end clamped between the auxiliary contact member 51 and the contact carrying arm 9 by one of the bolts 59. The intermediate portion of the flexible conductor 13 is secured at two points to the bridging member 55 by a pair of screws 15. The lower end of the flexible shunt conductor 13 is secured to the lower contact block 23 by means of a boli 11.

The switch member 5| has a yoke-shaped lower end which is pivotally mounted between the side walls of a main frame 19 by means of the pivot pin Si. The switch member 5| is movable about its pivot axis to open and closed circuit positions toV open and close the contact meansof the breaker by means of an operating mechanism indicated generally at 83. Y

The operating mechanism 83 is supported by the main frame 19 and comprises an actuating lever pivoted on a pin 81 carried by the frame, and is connected to the switch member 5| by a link-89. An operating member 9| is also pivoted on the pin 31 for movement about the Same axis as the actuating lever 85. The actuating lever is normally and relea'sably connected to the operating member 9| for movement thereby by means of a pair of latches 93 and 95, which are pivotally mounted on the lever 85 at 91 and 99, respectively. The latch 93 engages a roller |5| carried by the operating member 9|, and this latch is, in turn, held in latching position by the auxiliary latch 95. The operating member 9| is adapted to be releasablyheld in closed circuit position by means of a main holding latch |53 which releasably engages the roller |9I. The auxiliary latch 95 is provided with a curved tailpiece |15 by meansA of which it is released to cause release of the latch 93 and consequent tripping of the circuitA breaker by the release of the actuating lever 85 from its connection with the operating member 9|. When released the actuating member 85 moves in a counterclockwise direction about the pivot axis 81, causing opening of the movable contact means. During this movement, a cam surface |01 of the lever 85 engages the rounded nose of the main holding latch |93. moving the holding latch to released position to effect release of the operating member 9|. The switch member 5| and the actuating lever 85 lare biased to open position by means of a pair of accelerating springs |59 (only one being shown), which are connected at their upper ends to the switch member 5| and at their lower ends to the sides of the main frame 19.

To close the circuit breaker after it has been tripped open, the operating member-9|v is first moved in a counterclockwise direction about the pivot axis 91 to the open position to eiect resetting of the latches and reestablishment of the releasable rigid connection between the actuating lever 85 and the operating member 9|. After the rigid connection is thus established', the operating member 9| is moved in a clockwise direction to closed position by means of its handle to effect closing of the contact means of the breaker. When the parts have been moved to closed position, the main holding latch |03. reengages the Yroller |9| to hold the operating member in closed position. It will be noted that the construction of the operating mechanism is such that the movable contact means is trip free of the operating member 9|; that is, when the breaker is tripped, the contact means move to open positionirrespectiveV of the position of the operating member 9| Y The mounting arrangement of the contact means is such that during opening of the breaker the main bridging member 55 is first separated from the stationary contacts 25 and 2'1, while the auxiliary contacts remain inV engagement by reason of the outward movementV of the contact platform 33 under the influence of the biasing springs 11| and 43. After the bridging member 55 has separated a predetermined distance from the main stationary contacts; the intermediate contacts 29 and 69 begin to separate. This takes place assoon as the pins 35 engage the ends of the slots 31. During this time, the arcing contacts 3| and 1| remain in engagement due to the rocking movement of the contact platform 33. After the intermediate contacts haveseparated a predetermined distance, the arcing contacts 3| andV 1| begin to separate. During closing, the contacts engage in the reverseorder, as will readily be understood. It will thus be seen that the arc formed during separation of theV contacts is drawn only betweenthearcing An arc-extinguishing structure, indicated generallyat Il?, is mounted on the upper portion of the base for extinguishing the arcs drawn between the arcing contacts 3| and 1|. The arcextinguishing structure may be of any suitable type, but is preferably of the type fully described in Patent No. 2,243,938 of Leon R. Ludwig, issued May 1941, and assigned to the assignee of the present invention.

The circuit breaker is adapted to be tripped open either manually, or automatically in response to predetermined overload conditions in the circuit, by means of a trip device indicated generally at ||5.

The trip device comprises a trip lever 1 which is pivotally mounted intermediate its ends on the frame 19 by means of a pivot pin H9, and an electromagnet, indicated generally at |2|, which is operable in response to the predetermined overload conditions to move the trip lever |1 to tripping position to cause automatic opening of the circuit breaker.

One arm |23 of the trip lever ||1 is oiset and extends inwardly toward the base of the circuit breaker, and has its inner end disposed immediately above the electro-magnet |2| to be engaged and moved by a plunger of the electromagnet to effect automatic tripping of the breaker. The arm |23 of the trip lever is provided with a projection |25 which is adapted to engage the curved tailpiece |95 of the auxiliary latch 95 to move this latch to released position upon movement of the trip lever to tripping position. The other arm of the trip lever |1 forms a handle |21 whereby the trip lever may be manually moved to tripping position to effect manual opening of the circuit breaker. A spring |29 connects the arm |23 of the trip lever |1 to an extension or the main holding latch |93 so that the spring thus serves to bias the main holding latch to latching position and the trip lever to its normal position; as shown in Fig. 1.

The electromagnet i9! comprises a stationary core member ISI threadedly engaging a cross member |33 integral with the frame 19, and a movable armature |55. The movable armature |35 is slidable vertically in a guide comprising a sleeve |31 provided at its lower end with an annular flange which ts in a counterbore in the botto-m of a portion |39 of the main frame 19. The sleeve |31 is held in place by a member |4| secured 4by means of screws |133 to the bottom of the frame |39. The member |1|| is formed integral with a U-shaped frame which supports the time delay device and which is thus supported on the frame |39. A ilange on sleeve |41 integral with and extending downwardly from the member iM assists the sleeve |91 in guiding the movable armature |35. When the armature |35 is in its unattracted position (Fig. l) it rests on a pair of rollers |49 mounted on a pivot pin I5| which is supported in the sides of the U-shaped frame |55.

A seco-nd smaller armature |52 is disposed for vertical movement in an opening in the upper end of the armature |35. The armature |52 is provided with a shoulder which normally rests on a shoulder in the armature |35. A trip rod |54 rigidly secured tc the armature |52 extends upwardly therefrom. through an axial opening in the stationary core isi, the upper end of the trip rod being disposed beneath the end of the arm |23 of the trip lever 1. The second armature |52 is at times operated independently of the armature |35 to trip the breaker and at other times both the armature. |55 and the armature Cil |52 are operated together to trip the breaker as will be more fully disclosed later.

The pin |5| also pivotally supports a latch lever |53 which normally is in latching engagement with a latch member |55 screwed into an opening in the lower end of the armature |35. The armature |35 is thereby restrained in its unattracted position.

Also supported in the U-shaped frame |45 is a pivot pin |51 upon which is pivotally mounted a lever |59. Rigidly secured by means of a screw |b`| to oneend of the lever l 59 is an ambient temperature compensating bimetal element, |63. A current responsive thermal element |55 in the form of a bimetallic strip is rigidly mounted at its upper end by means of a screw |51 to a metallic block |59 which is secured in a recess in a conductor |1| having one end connected to the contact block 23 and the other end connected to the terminal |5 which in turn is connected to the terminal studs |9. The conductor makes a single loop around the magnet core |3| and |35 and the armature forms the energizing winding of the electromagnet.

Also mounted on the lever |59 is an adjusting knob |13 of insulating material having a screw insert |15 molded therein which threadedly engages the lower end of the lever |59. The inner end of the screw |15 bears against a yoke portion |11 of the U-shaped end of a lever arm |19 pivoted on the pivot pin |51. The arm |19 and the yoke portion |11 thereof are spaced from the sides of the frame |45 -by means of spacers |8| (Fig. 2). Mounted on the lever |59 by means of the screw |6| which secures the ambient cornpensating bimetal |53 to the lever, is a spring member |83 having its lower end engaging serrations formed on the inner periphery of the knob |'i3 to restrain the knob in its adjusted position. The upper end of the flat spring member |83 above the screw |5| is connected by means of a coil spring |85 to the lower end of the latch lever |53 below its pivot |5I. The spring |85 biases the assembly comprising the lever |59 compensating bimetal |63 and the knob |13 counterclockwise about the pivot pin |51 to the position where the end or the screw |15 engages the yoke |11 of the arm il'l. The arm |19 is prevented from counterclockwise movement by an ear |31 formed on the free end of the arm |19 resting against an adjusting screw |89 mounted in a bentover portion I9! of the latch lever |53 and locked in position by a lock nut |93. The spring |35 also biases the latch lever |53 in a counterclockwise or latching direction into latching engagement with the inside wall of the latch member |55. The force transferred from the spring |85 through the latch lever |53 to bias the latch lever counterclockwise to engage the latch with the latch member |55 is relatively light for the reason that the same spring |85 acting through the lever |59, screw |15, the arm |19 and the adjusting screw |99 applies a clockwise force to the latch lever. This latter force. however, is smaller than the torce which urges the latch lever in latching direction, therefore only the difference between the two forces acts to move the latch lever |53 connterclockwise or to latching position.

The bimetal element is insulated from the ambient compensating bimetal by means of an insulating butto-n |95 mounted in the upper end of the latter. Both of the bimetal elements |53 and |95 deect the same distance for a given change in ambient temperature. When the thermally responsive bimetal element |55 is heated in 7 response to overload currents by conduction from the increased resistance portion of thepconductor formed by the recess and block |69, the bimetal element deects toward the base Il of the breaker. During this deilection the bimetal |65 engages the insulating button |95 and rocks the compensating bimetal |63, the lever |59 and the arm |19 counterclockwise about the pivot |51. This movement of the arm |19 rocks the latch lever |53 clockwise about its pivot |5| thereby releasing the armature |35 whereupon the electromagnet, energized by the overload current traversing the energizing coil Vil, attracts the armature |35 and moves it upwardly against the stationary core iSl. The secondary armature |52 and trip rod |54 move upwardly therewith, the trip rod engaging the arm |23 and actuating the trip lever l'! to eect automatic opening of the breaker.

When the circuit is interrupted and the coil il! becomes deenergized, the armatures |35 and |52 are moved downwardly to their unattracted positions (Fig. l) by the force of gravity. As the bimetal |55 coo-ls and resumes its normal p osition, the spring 55 moves the latch |53 into latching engagement with the latch member |55 and, acting through the adjusting screw |89 restores the arm Ile, the lever |59 and the compensating bimetal |53 clockwise to the position shown in Fig. l.

Rotation of the knob |13 Varies the angular relation of the arm |19 and the compensating bimetal |53 and thereby varies the relation of the bimetal |53 with'the bimetal element |65. This varies lthe amount of time delay and current required by the bimetal |65 to unlatch the armature. A pointer lill integral withthe frame |45 cooperates with the knob |13 to indicate the calibration setting.

Upon the occurrence of a short circuit or an overload of approximately 1000% or more of normal rated current the electromagnet is energized a suicient amount to attract the secondary armature |52 and effect instantaneous tripping of the breaker independently of the armature |35 which remains latched in its unattracted position. Due to the relatively small mass of the secondary or short circuit armature |52, it will saturate during the operation and thereby prevent the generation of large magnetic forces which might cause damage to the device.

The circuit breaker including the trip device, may be used to interrupt circuits having various ampere ratings by substituting a series coil of the desired rating for the coil Il i. In order to provide substantially the same magnetic tripping force for the dierent ratings, the air gap between the armatures |35 and |52 and the stationary core |3| is adjustable in steps according to the selected ampere rating. The air gap of the trip magnet is adjusted by rotating the armature |35 relative to the latch member |55. Since the latch member |55, in its unattracted position rests on the rollers |49, rotation of the armature |35 will raise or lower the armature relative to the stationary core member 13| depending on the direction of rotation. The inner Wall ofthe latch member |55, including the latching surface, is made circular so that the latch |53 will engage the latch member irrespective of the position to Which it f is adjusted. The latch member |55 is provided with a tapped hole to receive a set screw |57 which extends through a selected one of a plurality of holes (only one being shown) properly spaced about the periphery ofarmaturel |35. The holes in the armature |35 allow the set screw |91 to engage the tapped hole in the latch member |55 in predetermined selected places corresponding to the current rating of the particular coil being used. For instance, when a series coil having a rating of say, 800 amperes, is mounted for use in the breaker, the armature |35 is rotated to bring the corresponding hole therein into alignment with the tapped hole in the latch member |55 after which the set screw |91 is replaced. In this manner the air gap of the trip magnet is adjusted for the particular value series coil Vwhich is used in the breaker.

Having described a preferred embodiment of the invention in accordance with the patent statutes, it is to be understood that various changes and modications may be made therein without departing from some of the essential features of the invention. It is, therefore, desired that the language or the appended claims be given as reasonably` broad interpretation as the prior art permits.

We claim as our invention:

1. In a circuit breaker comprising separable contacts and operating mechanism therefor, a trip device including a trip member, a solenoid having a stationary core member and an energizing winding, a plurality of movable core members having a common rectilinear axis of movement, means for positively holding one of said movable core members against movement, and a thermal element rigidly mounted on said winding to be heated thereby and operable in responsel to overload currents below a predetermined value ior operating said holding means to release said one movable core member and permit said core member to operate the trip member, the other movable core member being operable at times independently of said one movable core member to operate the trip member.

2. In a circuit breaker comprising separable contacts and operating mechanism therefor, a trip device including a trip member, an electromagnet having a relatively large armature, a relatively small armature supported by the rst named armature, means for positively holding the larger armature against operation, a thermal element supported on said electromagnet to be heated thereby and operable in response to overload currents below a predetermined value to release said larger armature and permit said electromagnet to operate both armatures to effect operation of the trip member, said smaller armature being operable independently of the larger armature in response to overload currents above said predetermined value to instantaneously operate the trip member.

3. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip member, an electromagnet comprising a core member and an energizing winding, a large armature and a relatively small armature disposed for axial movement along a common axis, means positively holding the large armature against operation, a thermal time delay device mounted on `said winding to be heated thereby and operable when heated a predetermined amount in respense to overload currents to release said large armature and permit the electromagnet to operate said large armature to eiect operation of the trip member, said small armature being at times operable independently of said large armature to instantaneously operate the trip member.

f 4. In a circuit breaker comprising'relatively ,L 9 movable contactsand operatingmechanism therefor, a trip device includingV a trip member, an electromagnet having an armature operable to operate said trip member, a latch member carried by said armature, means engaging said latch member for restraining said armature against operation, means for adjusting the armature relative to the latchfmember to vary the air gap of the electromagnet, and a bimetal velement operable when hea-ted a predetermined amount in response to overload currents to eiect release of the armature.

5. In a circuitbreaker comprising relatively movable contacts and operating mechanism therefor, a trip `device including ay trip member, an electromagnet, a relatively large armature, a re1- atively small armature mounted on and movable with the'large armatureia latch member rotatably mounted on the large armature, means engaging said latch member' to restrain said large armature against operation, time delay means including a bimetal element operable when heated a predetermined amount in response to certain circuit conditions to eiect reiease of the large armature and permit operation of. said armature to Operate the trip member, small armature being operable independently of the large armature in response to certain other circuit conditions to instantaneously operate the trip member, and said latch member being rotatable relative to said large armature to vary the magnetic air gaps of both armatures.

6. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip member operable to effect an operation of the operating mechanism, an electromagnet having a main armature, a second armature normally disposed in a recess in said main armature and operable thereby in response to certain circuit conditions to operate the trip member, said second armature being operable in response to certain other circuit conditions to operate the trip member independently of the main armature, and means supported on and movable relatively to said main armature for simultaneously adjusting the magnetic air gap of both of said armatures.

7. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip member, an electromagnet having an armature operable under certain circuit conditions to instantaneously operate said trip member, a second armature operable under certain other circuit conditions to cause said first named armature to operate the trip member, latch means for normally restraining said second armature against operation, an ambient temperature compensating bimetal mounted for movement independently of said latch means and operable to effect release of said second armature, and a thermally responsive bimetal operable when heated in response to overload currents to operate said ambient compensating bimetal.

8. In a circuit breaker comprising relatively movable contacts Vand operating mechanism therefor, a trip device including a trip member, a relatively large relatively small armature carried by said large armature and movable independently oi the larger armature, an electromagnet comprisint,r a stationary core member and a single energizing winding surrounding both of said armatures for moving said armatures, the larger armature when moved to attracted position moving the smaller armature l0 therewith to operate the trip member, and time delay means for controlling the movement of the larger armature.

9. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip member, a relatively large armature, a relatively small armature carried by said large armature, and operable independently of the large armature, a single energizing conductor surrounding both of said armatures for producing a magnetic eld for moving said armatures, the larger armature when moved to attracted position moving the smaller armature therewith to operate the trip member, time delay means for controlling the movement of the larger armature, and means mounted on and movable with the large armature for varying the air gap of both of said armatures.

10. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip member, a relatively large armature, a relatively small armature carried by said large armature, an electromagnet for moving said armatures, the larger armature when moved to attracted position moving the smaller armature therewith to operate the trip member, time delay means for controlling the movement of the larger armature, and a single means for simultaneously varying the air gap of both of said armatures.

11. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip member, a relatively large armature, a relatively small armature mounted on and movable with the larger armature to operate the trip member, an electromagnet comprising a fixed core member and a single energizing winding surrounding said core member and both of said armatures for moving said armatures, and a current responsive time delay device for controlling the movement of the large armature to attracted position, said smaller armature at times being movable independently of said larger armature to operate the trip member.

12. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip member, an electromagnet having an armature movable to operate said trip member, a pivoted latch normally restraining said armature against movement, an ambient temperature compensating bimetal element for operating said latch, load reducing means between said compensating bimetal and said latch, and a thermally responsive bimetal operable when heated a predetermined amount by overload currents to actuate said compensating bimetal element.

13. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip member, an electromagnet having an armature movable to operate said trip member, latch means normally restraining said armature against movement, an ambient temperature responsive bimetal element operable to effect release of said armature, biasing means comprising a spring between the latch and the ambient responsive bimetal disposed to apply a force biasing the ambient responsive bimetal in operating direction and to apply a force biasing said latch in latching direction, a thermally responsive bimetal element heated in response to overload current and operable when heated by overload currents to actuate the ambient temperature responsive bimetal, and means for transmitting themovement of said ambient temperature responsive bimetal to operate the latch to release the armature.

14.*Ina circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip member, an electromagnet lhaving an armature movable to operate said trip member, Alatch means normally restraining said armature against operation,

.operatingsaid trip member, a latch normally restraining said trip member against operation, a'spring disposed to apply a predetermined force to said latch biasing said latch in unlatching direction, said spring applying a greater force to said latch biasing said latch in latching direction, and current responsive means for operating said latch to release said trip member.

16. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip member, a re1- atively large armature, a relatively small armature carried by said large armature and operable independently of said large armature, said small armature saturating at certain value of overload current to prevent generation of large mechanical forces, and an energizing conductor for producing a magnetic eld for moving said armatures, the large armature being movable to attracted position in response to predetermined conditions and moving the small armature therewith to operate the trip member.

17. In a circuit breaker comprising relatively movable contacts and operating mechanism therefor, a trip device including a trip member, an electromagnet having an armature operable to operate said trip membena tubular latch member -adjustably connected to said armature, a latch engaging an annular latch surface on said tubular latch member for restraining said armature against operation, said latch member being rotatably adjustable relative to said armature to vary the magnetic air gap, and current responsive means for operating said latch to release said armature.

MERL E. HORN.

TURE LINDSTROM.

FRITZ E. FLORSCHUTZ. 

